Along with the development of high frequency electronic devices and the development of wireless networks and satellite communication devices, it has been a trend that information products have high speeds and high frequencies and that communication products transmit standardized voice, video and data wirelessly at large capacities and high speeds. Base boards required for new-generation communication products also have to fit the development trend thereof, and traditional FR-4 materials have been found difficult to meet the existing requirements. In a traditional process of fabricating a printed circuit board (PCB), if a high frequency signal will be used, the entire board has to be made of a material suitable for high frequency applications. If the high frequency signal is required to be used on a portion of a board (generally in an area less than one third of the entire board), only a portion of the board would use the high frequency material (generally in an area less than one third of the entire board) to reduce the usage amount of the costly high frequency board material, thus greatly reducing the cost of a PCB.
Also, only a fraction of electric energy consumed by electronic elements in operation is used to drive the electronic elements, and most of the electric energy is transformed into heat. The heat rapidly increases the temperature of the electronic elements. If the heat is not timely dissipated, the temperature of the electronic elements might constantly increase, thus resulting in decreased reliability and even failure of the electronic elements due to being overheated. It may not be sufficient to depend on self-dissipation of heat for an electronic element generating a large amount of heat. One method to address the issue of heat dissipation of a high power device is to bury a copper conductor in the board. A board having a portion of hybrid lamination and a buried copper conductor may solve the issue of high frequency signal transmission delay and heat dissipation of a high power device. With these structures, the board may meet the requirements of electrical performance of a product and the cost thereof can be saved.
There are two conventional methods for fabricating a board having a portion of hybrid lamination and a buried copper conductor:
The first method is a Mas Lam lamination process. This method includes a process of bonding individual base substrates with gel/resin to form boards and a process of stacking the boards. An arrangement of bonding individual base substrates with gel/resin may be: L1/L2 base substrate-resin layer-L3/L4 base substrate-resin layer-L5/L6 base substrate-resin layer-L7/L8 base substrate-resin layer-L9/L10 base substrate-resin layer-L11/L12 base substrate. A process of stacking the bonded boards may be: (1) preparing a bonded board; (2) burying copper conductor in the board; (3) attaching a release film to the board; (4) attaching an aluminum sheet to the board; (5) attaching a steel sheet to the board; (6) turning the board over; (7) burying a high frequency sub-board in the board; (8) attaching another release film to the board; (9) attaching an aluminum sheet to the board; and (10) attaching a steel sheet to the board.
The second method is a Pin Lam lamination process, i.e., a method of directly stacking boards. In a laminating process of, for example, a 12-layer (12L) board having a portion of hybrid lamination and a buried copper conductor, layers in the board may be arranged in the following order: steel board-aluminum sheet-release film-L12/L11 base substrate-high frequency sub-board-resin layer-L10/L9 base substrate-resin layer-L8/L7 base substrate-resin layer-L6/L5 base substrate-resin layer-L4/L3 base substrate-resin layer-L2/L1 base substrate-buried copper conductor-release film-aluminum sheet.
In the first method, two processes as described above have to be performed, and the board has to be flipped over in the board stacking process. This may potentially result in an inefficient production, a considerable amount of labor, and instable product quality.
In the second method, boards may not necessarily be pre-bonded because a Pin Lam processing equipment will perform the alignment among base substrates and elements using pins. But the Pin Lam processing equipment is expensive and may be inefficient and costly.